The mixing of liquids in controlled proportions is the keystone of many applications, a primary example of which is liquid chromatography. In a liquid chromatography application, a pump module intakes and delivers a mixture of liquid solvents and an injected sample to a point of use, such as a column of particulate matter. By passing the mixture through the column, the various components in the sample separate from each other at different rates and thus elute from the column at different times. A detector receives the elution from the column and produces an output from which the identity and quantity of the analytes may be determined. In an isocratic chromatography application, the composition of the liquid solvents remains unchanged, whereas in a gradient chromatography application, the solvent composition varies over time.
The reliability of the results produced by a chromatography application depends heavily on run-to-run reproducibility. In particular, the identification of sample analytes depend on the retention times of the detected elution peaks. Some pumping systems exhibit non-ideal pump characteristics, such as fluctuations in solvent composition and fluctuations in flow rate. These non-ideal pump characteristics can lead to undesirable separation performance and unreliable run-to-run reproducibility. In general, the greater the intake velocity of a pump module, the lower is the accuracy of solvent composition because of pump errors, such as bubble formation (outgassing) and timing errors related to valve switching. Accordingly, the benefits of a low intake velocity are a reduction in time-based errors and in pressure drop, thus in the out-gassing and cavitation of the intake fluidics.